It is known to subject the water flowing in a conduit or a network of conduits, to treatment adapted to disinfect it, which is to say to eliminate the microorganisms which it carries.
To this end, a first solution consists in introducing into the water chemical agents, such as chlorine or chlorine derivatives. However, this type of chemical agent has several drawbacks.
Thus, once introduced into the water, the latter lead to the formation of biproducts of chlorination, such as organo-chlorine products, which are undesirable substances, whose accumulation in the conduits carrying the water for human consumption, is likely to give rise to problems of public health.
Moreover, it has been noted that chlorine gives rise to internal corrosion of the conduits of the network, thus creating cavities in the walls of the conduits which promote the deposit, growth and propagation of a biofilm of microorganisms.
Moreover, it has been noted that certain pathogenic germs resist the action of chlorine and its derivatives.
An alternative to the use of chlorine derivatives is the use of ozone or an ozonated gas injected directly into the water to be treated.
Thus, the fact of sending ozone into a conduit colonized by bacteria limits the development of these latter and improves the quality of the water. In other words, the ozone permits reducing the living bacterial flora carried by the water to a threshold below the detectable limit. These variable doses used do not give rise to the formation of biodegradable dissolved organic carbon (BDOC), which serves to nourish the bacterial flora; the risks of revival of the microorganisms are hence reduced.
Moreover, the breakdown of the ozone does not lead to subproducts adapted to harm public health and does not give rise moreover to any problem of corrosion of the pipes.
Another problem to which it is necessary to give attention, is that of the progressive deposits on the internal wall of the pipes by deposit on the latter of ions carried by the water. This deposit is greater when the conveyed water is warm because the temperature favors shifting the calco-carbon equilibrium, leading to calcarious deposits.
Such ionic deposits leading to the formation of scale in the pipes are undesirable because on the one hand they give rise to progressive clogging of the pipes and on the other hand they favor and facilitate the implantation and growth of a biofilm of microorganisms.
To limit these scaling phenomena, it is necessary to bring the water to calco-carbonic equilibrium, which is effected in a known manner by either restoring the equilibrium of the water with salt, or, as the case may be, changing the pH.
Conventionally, the re-equilibrating water with salt requires a complex and costly material, whose principal operation is based on ion exchange technique, whilst requiring the use of a large quantity of reagent. If this technique permits solving at least partially the problem of scaling in pipes, it also gives rise to untimely development of microorganisms.
Changing the pH, and hence the calco-carbonic equilibrium toward acid pH, can be carried out itself by introduction into the water to be treated of strong acids, such as 97% sulfuric acid or 35% hydrochloric acid, or a weak acid. However, the use of acid products gives rise to several drawbacks, namely, their handling is difficult and potentially danger for the user, the acids are a source of pollutant ions for the water (SO.sub.4.sup.2-, Cl.sup.- ions . . . ), the acidity is a cause of corrosion of pipes, the doses added to the water must be very carefully controlled so as to avoid any risk of over or under acidification of the water.
An alternative to the use of acids or salts consists in the dissolution in the water to be treated of carbon dioxide (CO.sub.2), which permits reducing the pH of the water effectively, easily and stably.
Moreover, when it is desired to treat water flowing in a pipe, which water carries microorganisms and ions promoting scaling in the pipe, it is recommended to inject ozone (O.sub.3) therein, and carbon dioxide (CO.sub.2). Thus, in this way, there is a synergetic action of the two gases.
More particularly, the ozone will permit eliminating the microorganisms carried by the water and the CO.sub.2 will prevent or slow the formation of scale and hence the deposit of the biofilm of microorganisms on the internal walls of the pipes.
The injection of ozone and carbon dioxide into water to be treated can be carried out either by injecting these two gases independently of each other, or by using a preliminary mixing of them, thus we will speak of simultaneous injection of the two gases.
The field of application of this type of water treatment process is very wide and relates particularly to the hospital field (fighting nosocomial infections due to Legionelle, Pseudomonas . . . ), or generally: the protection of piping against clogging due to scaling and to the deposit of biofilm on their internal walls, and the industrial sector: treatment of water for subsequent processes, combatting clogging of piping and heat exchangers . . . .
Until now, numerous processes disclosing treatment of water with ozone gas and/or carbon dioxide have been described and there can be cited or example EP-A-0 567 860, WO95/13989, U.S. Pat. No. 5,085,809, JP-A-04 90891.